My own view is that Kant's conception of the duality of the good (morality and happiness, the good of our person and the good of our state or condition) is a distinctively modern view.

Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.

Fichte takes an I or free will to be not a thing or being but an act which is not undetermined but self-determined, in accordance with reasons or norms rationally self-given.

It is actually a nice question how far Descartes himself endorses the monological and metaphysically dualistic theory of mind associated with his name and his legacy in early modern philosophy. But Fichte does reject this tradition, by suggesting that an immaterial thinking substance is an incoherent notion, and a rational being whose rationality was not developed through communication with others is a transcendental impossibility.

Fichte is a necessary step to both Hegel and Marx.

In fact people do not know enough about themselves and what is good for them to form a sufficiently definite conception of the general happiness (or whatever the end is) to establish definite rules for its pursuit.

Clearly no working class movement ever came about that was able to do what Marx was hoping for.